The present invention relates to a process for the production of fumaric acid by the isomerization of maleic acid at high conversions which comprises heating maleic acid in the presence of phosphoric acid at a temperature sufficient to isomerize the maleic acid to fumaric acid. The process provides high purity fumaric acid in good yields.
Fumaric acid us used in the manufacture of paper sizing resins; as a food additive, especially as a food acidulant in products such as fruit juices, gelatin desserts, and animal feed; in unsaturated polyester resins; in alkyd coatings; in the manufacture of inks, and in other applications. Purity of the fumaric acid is particularly important when it is used as a food additive.
Fumaric acid has been traditionally produced by isomerization of maleic acid in water in the presence of catalysts such as bromine, bromide, sulfuric acid, hydrochloric acid and thiosulfites. A disadvantage of these processes is that the agents used as catalysts and co-catalysts have adverse effects on the environment, cause serious disposal problems, and require further purification of the fumaric acid to convert it into a product with acceptable, odor, color, and quality. These all add significantly to the costs of producing fumaric acid, particularly fumaric acid of food grade quality, which is the quality usually preferred.
SU273818 discloses a method of producing fumaric acid by using a strong acid and one or more catalysts, such as ammonium bromide, ammonium persulfate, ammonium bromide, ammonium persulfate, or thiourea to isomerize aqueous solutions of maleic acid. The strong acids, for example, sulfuric, hydrochloric, orthophosphoric, oxalic and other acids that are as strong as maleic acid are introduced into the maleic acid solution along with the catalyst prior to isomerization. The isomerization is conducted at 65-80.degree. C., optimally at 70-72.degree. C.
CS 250 620 B1 discloses a process for producing fumaric acid in the presence of hydrochloric acid as the catalyst wherein the reaction mixture formed of maleic acid and hydrochloric acid with a concentration of 50-90 wt % maleic acid, calculated from maleic anhydride and water, and up to 20 wt % hydrochloric acid, 33-37% relative to the amount of maleic anhydride used, is heated to boiling at pressure of 0.2-2 MPa for a time of 0.25-8 hours, followed by isolation of the fumaric acid from the reaction mixture.
U.S. Pat. No. 2,393,352 discloses a process of manufacturing fumaric acid from maleic anhydride-containing converter gases by absorbing the maleic anhydride vapors in aqueous mineral acid solutions, such as hydrochloric acid, hydrobromic, acid hydroiodic acid, and sulfuric acid. Nitric acid is disclosed to be useable but less desirable due to its oxidizing tendencies. The maleic anhydride gases are cooled to 40.degree. C. to 60.degree. C. (but not below the dew-point of the gaseous mixtures with respect to maleic anhydride) so as to avoid raising the temperature of the hydrochloric acid solution to its boiling point. The resulting hydrochloric acid solution may be heated to 80.degree. C. to 100.degree. C. in order to complete the conversion of the maleic acid present to fumaric (in admixture with the precipitated fumaric acid or after removal of the precipitate). However, it is noted that unless equipment is provided for the recovery of mineral acid and its maintenance in the Absorber (e.g., by the use of superatmospheric pressure) certain of the beneficial advantages of the preferred process will not be obtained, such as efficient reuse of the mineral acid.
U.S. Pat. No. 2,816,922 discloses a process for the production of fumaric acid from aqueous maleic acid liquors, particularly those resulting from the production of phthalic anhydride, involving the steps of heating in a conversion zone a concentrated maleic acid liquor, that is, one from which a major proportion of the water has been removed, to vaporize additional water and to convert the maleic acid into fumaric acid. In a more specific embodiment, the process for noncatalytically converting maleic acid contained in relatively dilute aqueous maleic acid solutions containing up to about 30% by weight of maleic acid to fumaric acid, comprises heating the dilute maleic acid to an elevated temperature below about 250.degree. F. in a concentration zone to evaporate water from the dilute solution and produce a concentrated maleic acid solution containing about 70-90% by weight of maleic acid, heating the concentrated maleic acid by raising the temperature of the liquor, preferably by submerged combustion, to a temperature above 250.degree. F. and below about 400.degree. F. in a conversion zone to produce a slurry of fumaric acid in aqueous maleic acid, withdrawing a vapor stream comprising steam and maleic anhydride from the conversion zone and passing it into the concentration zone, withdrawing said slurry from the conversion zone, diluting the withdrawn slurry with concentrated maleic acid solution, separating the diluted slurry into a liquid phase comprising aqueous maleic acid and a solid phase comprising crude fumaric acid and returning the liquid phase to the conversion zone. A disadvantage of this process is that the crude fumaric acid contains impurities, such as phthalic acid, and must be further treated to purify it. The purification treatment requires subjecting the crude fumaric acid to a decolorization process using, e.g., carbon, then separating the carbon, recrystallizing the fumaric acid, and drying it.
U.S. Pat. No. 2,816,923 discloses a process for the production of fumaric acid from aqueous maleic acid liquors, particularly those resulting from the production of phthalic anhydride, involving the steps of heating in a reaction zone a maleic acid liquor to form a top vapor phase of maleic anhydride, and a bottom fraction of fumaric acid crystals in a maleic anhydride melt. The top vapor phase and water pass into an adsorption zone wherein the maleic anhydride is absorbed and the water is allowed to escape from the system. The bottom fraction is joined with fresh maleic acid feed as it issues from the reaction zone, and the resulting aqueous stream is introduced into a separation zone, wherein the crude fumaric acid crystals are separated and the liquid passed into the adsorption zone wherein the maleic anhydride is scrubbed from the vapors or absorbed by the liquid, the resulting mixture then going into the reaction zone. A disadvantage of this process is that the separated crude fumaric acid crystals contain impurities, such as phthalic acid, and must be purified in additional process steps. The purification treatment involves decolorization, recrystallization, and drying.
Applicant has made the surprising and unexpected discovery that maleic acid can be isomerized at high conversions to give fumaric acid of excellent color and quality by heating the maleic acid in the presence of phosphoric acid under conditions suitable to cause isomerization of the maleic acid to fumaric acid. The fumaric acid product can be recovered by filtration or other means. Such a process conveniently makes a fumaric acid product in a yield of at least about 30 wt %, preferably at least about 50 wt % yield, more preferably at least about 60 to about 80 wt % yield, even more preferably at least about 90 wt %, still more preferably at least about 95 wt %, yet more preferably, at least about 98 wt %, and most preferably at least about 100 wt %. The fumaric acid product can optionally be further purified by washing with water. It is unexpected that the isomerization of maleic acid to fumaric acid can be conducted using phosphoric acid without the addition of catalysts.
The present invention advantageously provides a process for making very high purity fumaric acid by isomerizing maleic acid at high conversions to give fumaric acid of good quality and color without the need to add undesirable catalysts. The fumaric acid is easily recovered by filtration or other means, and a simple water wash almost completely removes any remaining phosphoric acid so that the fumaric acid product is readily purified.
The mother liquor is completely recyclable for use in consecutive reaction batches. Because the only components used in the reaction mixture are maleic anhydride and/or maleic acid, phosphoric acid, and water, it is believed that the process of the present invention will meet the stringent requirements for producing food grade fumaric acid, and that the process is more environmentally acceptable than known processes for making fumaric acid.
The exclusive use of phosphoric acid in the present invention has the advantages of permitting the complete recycling of the mother liquor from the reaction, and mitigating the environmental hazards associated with catalysts, such as bromine, thiourea and its derivatives, thiosulfate, potassium thiocyanate, colloidal sulfur, hydrogen sulfide and sulfuric acid together, hydrohalic acids, ammonium bromide, ammonium persulfate, thiourea etc. which have previously been used for isomerizing maleic acid to fumaric acid. Use of chloride containing compounds, such as hydrochloric acid, as catalysts for the reaction may cause corrosion of the reactor metal as may the use of harsh oxidizing acids such as hydrobromic acid, hydroiodic acid, sulfuric acid and nitric acid. With chloride-containing acids such as hydrochloric acid, there may also be a possibility of formation of chlorinated hydrocarbon by-products which is undesirable.
The fact that in the present invention the mother liquor can be recycled also has the advantage of reducing costs. Since chlorinated hydrocarbon byproducts and other undesirable by-products are not formed in the process of the present invention, the mother liquor from the reaction can be recycled and used to prepare additional fumaric acid. This provides a cost advantage since phosphoric acid supply costs and disposal costs are greatly reduced.
Another advantage of the process of the present invention is that the process can be conducted at high temperatures without the use of pressure equipment such as an autoclave. This reduces costs since it avoids the need to purchase equipment for conducting the process under pressure and also provides for a more convenient process. The high temperatures and pressures required in other processes require the use of cumbersome and expensive production installations such as high-pressure autoclaves.